The present invention relates to a method and an apparatus for filling a pressure tank with a fluid.
Such methods and apparatus are known, for example, in systems for coating substrates, such as CDs.
With these systems, a lacquer that is disposed in a pressure tank is moved via a riser to a coating station by the pressure that is in the pressure tank. At the coating station, the lacquer is applied to the CDs that are to be coated by means of an outlet or discharge valve. In this connection, for a uniform and continuous coating of these CDs it is important that the pressure of the lacquer that is to be dispensed at the outlet valve preferably have a constant predetermined value.
With the heretofore known systems, however, such a uniform and continuous coating of these CDs was not possible during the filling or refilling of the pressure tank with lacquer, so that the coating process had to be interrupted during the refilling process. During the filling or refilling of the pressure tank with lacquer, the pressure tank was relieved to ambient pressure and the lacquer was then introduced into the tank via a fill opening. However, with this procedure undesired interruptions of the coating processes, as well as a high consumption of nitrogen, which is generally utilized, resulted in order to again bring the pressure tank to the desired pressure after the filling process.
It is therefore an object of the present invention to enable filling of a pressure tank with a fluid without the necessity for interrupting the use of the pressure tank.
The stated object is inventively realized by a method for filling a pressure tank with a fluid from a refill tank that is disposed higher, whereby the tanks are interconnected by a gas connecting line and a fluid feed line, by regulating or adjusting the pressure in the pressure tank via a proportional valve that is disposed in a gas inlet line of the pressure tank, while the connecting lines to the refill tank are closed, by adjusting the pressure in the refill tank to the pressure in the pressure tank, and by opening the connecting line between refill tank and the pressure tank. By adjusting the pressure in the refill tank to the pressure in the pressure tank it is possible to fill the pressure tank with fluid without having to first relieve the pressure. Furthermore, the pressure conditions within the pressure tank are not changed by the filling process, since the same pressure exists in both tanks, so that the function and the use of the pressure tank are not adversely affected. Since the refill tank is disposed higher than the pressure tank, there is a hydrostatic pressure difference that causes the fluid to run into the pressure tank without thereby changing the gas pressure within the pressure tank.
Pursuant to a preferred specific embodiment of the present invention, the gas inlet line between the proportional valve and the pressure tank is closed prior to adjusting the pressure in the refill tank, and the regulation or adjustment of the pressure in the refill tank is effected via the same proportional valve that is used for regulating the pressure in the pressure tank. This results in the advantage that for the regulation of the pressure in the refill tank the same components are used as for the regulation of the pressure tank without thereby adversely affecting the pressure in the pressure tank. Although a readjustment of the pressure in the pressure tank is not possible during the regulation of the pressure in the refill tank, a critical pressure change within the pressure tank that limits the function of the pressure tank lasts longer than does the adjustment of the pressure in the refill tank to the pressure in the pressure tank. After reaching the same pressure in the refill tank, the gas inlet line can again be opened, so that no adverse impact upon the system occurs as a result of the brief closing.
The pressure in the pressure tank is advantageously adjusted to a desired pressure value that is determined as a function of measurement results of a first pressure sensor that is disposed in an outlet line of the pressure tank, in order to achieve an automatic adaptation of the system to variable disturbance factors, such as the filling height of the fluid in the tank as well as filter pressure losses of a filter that is typically disposed in the outlet line. In this connection, the desired pressure value is advantageously not altered as long as the gas inlet line between the proportional valve and the pressure tank is closed, since a readjustment of the pressure in the pressure tank at this point in time is not possible, and a change of the desired pressure value would lead to adjustment of the refill tank to a pressure that is different than that of the pressure tank. This would lead to undesired pressure fluctuations or changes when the connecting line between the refill tank and the pressure tank is opened.
The pressure in the gas inlet line is advantageously measured in order to provide the actual pressure that is required for a regulation of the pressure in the pressure tank or of the pressure in the refill tank. The measurement of the actual pressure in the gas inlet line has the advantage that the same pressure sensor is used for the pressure tank as well as for the refill tank, as a result of which a greater precision can be achieved and the cost for an additional pressure sensor can be saved. Furthermore no dynamic line and/or filter pressure losses occur in the gas inlet line, so that a stable regulation condition of the proportional valve is achieved without fluctuations.
Pursuant to a further, preferred specific embodiment of the invention, the desired pressure value is determined as a function of a differential pressure sensor as long as the connecting lines between the refill tank and the pressure tank are opened; this differential pressure sensor is disposed between the gas inlet line and the outlet line of the pressure tank. By using a differential pressure sensor between the gas inlet line and the outlet line of the pressure tank, the filling state height that varies during the filling can be taken into account, and the desired pressure value can be accordingly adjusted. Furthermore, the use of a differential pressure sensor enables an automatic indication when the filling process is concluded.
The object of the present invention is also realized by an apparatus for filling a pressure tank with fluid from a refill tank that is disposed higher, whereby the tanks are interconnected by a gas inlet line and a fluid feed line, according to which the apparatus is provided with a proportional valve in the gas inlet line to introduce a pressurized gas into the pressure tank, a first valve that is disposed between the proportional valve and the pressure tank, a second valve that is disposed between the proportional valve and the refill tank, and a third valve that is disposed in the fluid feed line. Such an apparatus again makes it possible to bring the pressure within the refill tank to the same pressure that exists in the pressure tank without thereby affecting the pressure in the pressure tank. Subsequently, a connection can be established between the refill tank and the pressure tank, so that the fluid that is in a refill tank can flow into the pressure tank due to a hydrostatic pressure difference, without altering the gas pressure ratios in the pressure tank.
Preferably provided in an outlet line of the pressure tank is a first pressure sensor, which is in communication with a control unit that with the aid of the measurement results of the pressure sensor determines a desired pressure value for the proportional valve. As already indicated previously, this enables an adaptation of the system to variable disturbance factors, such as tank filling state and filter pressure losses. The apparatus preferably has a second pressure sensor that is disposed in the gas inlet line in order to provide an actual pressure value for a regulation of the proportional valve, which value is not influenced by dynamic line and filter pressure losses.
The apparatus is preferably provided with a differential pressure sensor between the gas inlet line and the outlet line in order during the filling of the pressure tank with the fluid to enable an automatic adaptation of the system parameters to the changing tank filling height.
Pursuant to a further, preferred specific embodiment of the invention, the refill tank can be connected via coupling elements to the gas inlet line and to the fluid refill line. This makes it possible to fill the refill tank remote from the pressure tank, and in addition the refill tank can be used for the sequential filling of a plurality of pressure tanks. In this connection, the coupling elements are advantageously provided with sensors that provide an automatic indication when the coupling elements are closed. Pursuant to one specific embodiment of the present invention, the second and third valves can be automatically closed by release of the coupling elements in order not to adversely affect the system of the pressure tank in the event that the coupling elements are inadvertently released. The coupling elements are preferably quick or snap-type couplings.